1. Field of the Invention
The present invention relates to a solid-state image sensing device for endoscopes for picking up endoscopic images and to an improved endoscope imaging apparatus.
2. Description of Related Art
In an electronic endoscope apparatus of a frame-sequential type, information obtained from the effective number of pixels of the CCD is processed and output as it is with respect to the three-primary-color signals of R (red), G (green) and B (blue). That is, theoretically, the resolution is the same for R, G and B.
In electronic endoscope apparatuses of a simultaneous type and external TV cameras, a color chip filter is provided on the front surface the CCD. Therefore, the resolution (frequency band width) for R and B is theoretically poorer as compared with that for G. Further, the number of R-color filters is the same as the number of B-color filters, and, in the signal processing system, the processing of the same band width is performed for R and B, so that the resolutions for R and B obtained from the CCD are theoretically the same.
In a 3-plate external TV camera, the resolution is theoretically the same for R, G and B. The resolution may be enhanced by increasing the number of pixels in the CCD. However, an increase in the number of pixels would lead to an increase in the size of the head section of the external TV camera and that of the front end section of the electronic endoscope, resulting in poor operability. Further, an increase in the number of pixels of the CCD would require an increase in memory capacity, resulting in an increase in the size of a CCU (camera control unit) for processing the output signals of the TV camera and controlling the TV camera.
In an endoscopic image, the amount of G-information is the largest, and that of B-information is the second largest, the amount of R-information being relatively small as compared with those of G and B-information.
Generally speaking, studies are being made regarding the development of image pick-up apparatuses, inclusive of endoscope imaging apparatuses, which are capable of providing a high-resolution image. One subject for such studies is the reduction of the size of the camera head section and that of the front end section of the electronic endoscope. In particular, in the endoscopic field, there is an urgent demand for reducing the diameter of the endoscope front-end section from the viewpoint of improving the insertion property and operability of the endoscope and of reducing the examination time. Further, there is also a demand for a reduction in the memory capacity of the signal processing system for processing image pick-up signals from the viewpoint of attaining a reduction in cost, apparatus size, etc.